An important aspect of mixed critical systems is to execute tasks of varied criticality on the same platform. The property of full or partial reconfiguration at runtime of reconfigurable hardware or field programmable gate arrays (FPGAs) has satisfied this criterion and facilitated the processing of mixed critical tasks directly on hardware, with the aid of reconfigurable intellectual properties (IPs) or bitstreams procured from various third party IP (3PIP) vendors. However, the existing literature in this arena does not consider the associated hardware threats. Such threats are particularly dangerous as related malware like Hardware Trojan Horses (HTHs) remain dormant during testing and evade detection, but get activated at runtime and jeopardize mission critical applications. Though several works exist on hardware security, none focus on reliability driven mixed critical task processing on reconfigurable hardware against HTH attacks. In this work, we initially explore how HTHs implanted by 3PIP vendors in the bitstreams may cause active attacks. Then, we develop strategies to ensure reliability for processing of mixed critical tasks on reconfigurable hardware. Both periodic and non-periodic, i.e. aperiodic or sporadic tasks are considered. We also focus on resource constrained environments, where we adhere to frequency scaling to facilitate accommodation of tasks on limited resources. We experiment with a variety of bitstreams and performance evaluation is performed via metrics such as task success rate, task rejection rate and task preemption rate. © 2019